1. Technical Field
The present invention relates in general to an improved structural member, and in particular to an improved structural beam, made by joining dissimilar materials. Still more particularly, the present invention relates to a structural composite preform for joining the web of a structure with a second member formed from dissimilar materials.
2. Description of the Prior Art
Structures that require strength and a light weight may have dissimilar materials joined to each other. For example, an aircraft may have a composite panel or skin that is secured to an metal beam, such as of aluminum. Prior approaches to joining dissimilar materials such as metals and composites have generally relied on mechanical fastening if the two elements are at an angle. As shown in FIG. 1, a spar 1 having an inverted T-shaped metal plate 3 with a flange 5 is joined to a flat composite panel 7 with mechanical fasteners 9 such that metal plate 3 and composite panel 7 are perpendicular to each other. In such an arrangement, metal plate 3 must have a flange 5 to enable fastening to composite panel 7. The necessity of having flange 5 on metal plate 3 adds considerable cost to its fabrication since flange 5 significantly increases the volume of metal that must be purchased and then machined away. In addition, mechanical fastening involves drilling and countersinking holes, installing fasteners and, in some cases, treating the fastener heads to achieve a desired surface smoothness. These steps are expensive and can contribute an additional 25% to 60% to the overall cost of the spar assembly. Thus, an improved apparatus and method for forming a structural support member by joining dissimilar materials at an angle is needed.
A preformed component or xe2x80x9cpreformxe2x80x9d for joining a first member to a second member of dissimilar materials has a planar base with two longitudinal legs extending in parallel therefrom. A channel is defined between the legs of the preform, and the first member, such as a flat metal plate that forms the web of the structural support member, is inserted into the channel. The base of the preform is bonded to the second member, typically a composite panel.
The preform is a composite material having continuous filaments of woven or braided fiber. The preform is impregnated with a thermoset resin that joins and bonds the first and second members to each other. The preform provides excellent structural support even if the first and second members are formed from dissimilar materials such as metal and composite. The resin is structurally reinforced with oriented fibers in such a manner as to provide coupling strength between the joined members.
When a single filament is chosen for the preform, its properties are selected to minimize the difference in thermal expansion coefficients of the metal web and the composite flange. However, the preform may have two or more types of filaments with different properties. The filament in the base of the preform is chosen such that its axial thermal expansion coefficient matches that of the composite flange. The filament in the legs of the preform is chosen such that its axial thermal expansion coefficient matches that of the metal web. These filaments are used in combination to provide coupling strength between the joined metal web and composite flange by having the best structural fiber oriented parallel to the legs of the preform, and by its being interwoven into the base of the preform.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.